The exhaust gas emitted from an internal combustion engine is a heterogeneous mixture that contains gaseous emissions such as carbon monoxide (“CO”), unburned hydrocarbons (“HC”) and oxides of nitrogen (“NOx”) as well as condensed phase materials (liquids and solids) that constitute particulate matter (“PM”). Catalyst compositions typically disposed on catalyst supports or substrates are provided in an engine exhaust system to convert certain, or all of these exhaust constituents into non-regulated exhaust gas components.
One type of exhaust treatment technology for reducing CO and HC emissions is an oxidation catalyst (“OC”) device. The OC device includes a flow-through substrate with a catalyst compound applied to the substrate. The catalyst compound of the OC device induces an oxidation reaction of the exhaust gases once the OC device has attained a threshold or light-off temperature. One type of exhaust treatment technology for reducing NOx emissions is a selective catalyst reduction (“SCR”) device. The SCR device includes a substrate, where a SCR catalyst compound is applied to the substrate. A reductant is typically sprayed into hot exhaust gases upstream of the SCR device. However, the SCR device also needs to reach a threshold or light-off temperature to effectively reduce NOx. Following a cold start of the engine, the OC device and the SCR device have not attained the respective light-off temperatures, and therefore generally may not effectively remove CO, HC, and NOx from the exhaust gases.
One approach for increasing the effectiveness of the OC and the SCR devices involves providing an electrically heated catalyst (“EHC”) device upstream of the OC device and the SCR device. The EHC device includes a monolith and an electrical heater. The electrical heater of the EHC device is heated to a respective light-off temperature, which is the temperature at which rapid HC oxidation occurs within an oxidation catalyst compound disposed on the EHC device, and also provides heat to the OC and the SCR devices as well.
In one approach, the EHC device may be powered by a generator. The generator has an internal resistance, which is referred to as the resistance of the generator. The amount of electrical power transferred to the EHC device from the generator reaches a peak when a load resistance (e.g., the resistance of the EHC device) is generally the same as the resistance of the generator. Accordingly, it is desirable to provide an approach for effectively providing electrical power to the electrical heater of the EHC device.